3-Mercapto-1-Propanesulfonate for Cu Electrodeposition Studied By in Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS)

Damascene processing of copper interconnects for integrated circuits requires void-free filling of high aspect ratio trenches and vias.  A combination of organic additives is commonly used to achieve bottom-up or superfilling of these features by electrochemical plating.  To better understand the surface interactions of brightening agents, 3-mercapto-1-propanesulfonate (MPS) was studied by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS).  The influence of each functional group was discerned by individually testing butanethiol and butanesulfonate as model compounds.  In an acidic solution of copper sulfate, MPS coadsorbs with sulfate.  Butanethiol displays similar adsorption behavior, but butanesulfonate demonstrates no Raman bands attributed to surface adsorption.  This strongly suggests that the sulfonate moiety does not interact significantly with the Cu substrate, and MPS adsorption occurs through the thiol linkage.  When chloride is added, sulfate is displaced and both MPS and butanethiol coadsorb with the halide.  However, the Cu-Cl stretching vibration is weaker in the presence of these additives than it is with Cl- alone.  In addition to spectroelectrochemical experiments, Cu deposition processes with these additives were also monitored by electrochemical quartz crystal microbalance measurements.  Butanethiol is more resistant than MPS to both Cu deposition and stripping, which confirms that the sulfonate group plays an important role in facilitating Cu deposition.